The animals of Eurasia - Реферат

Рефератна тему:THE ANIMALS OF EURASIAEurasia is the largest land mass on earth, stretching halfway around the globe from the British Isles to the Pacific Ocean, and from the Bering Sea south to the tip of Malaysia, an area of 54 million sq km (21 million:sq -л"ХА few of its animal species, especially those in the north, are closely related to, and in some instances are the same as, those of North America.Relatively recently, as earth time is measured, Eurasia was linked to America by a land bridge which spanned what is now the Bering Straits. This causeway existed for thousands of years during the Ice Ages, when much of the earth's water was locked up in glaciers, thus lowering sea level. Animals crossed back and forth between the two continents on the land bridge, and the first human settlers in America probably arrived via this route.About ten thousand years ago, the latest in a series of ice ages came to an end. The ice melted; the seas rose, and the Bering land bridge was submerged. Animal species which had wandered west into Eurasia or east to America were isolated from their native homelands. But because ten thousand years is a mere eye wink in evolutionary timekeeping, very few changes have had time to take place in these exiles. For example, the largest member of the deer family lives in the taiga of both Eurasia and America. In Eurasia it is called an elk, in America, a moose. But it is one and the same animal. This is also true of another deer, the caribou, or reindeer. The former is a wild animal of America; the latter has been domesticated for centuries by the Lapps of northern Europe.The Bering land bridge was probably responsible for the survival of at least one species - the horse. This animal originated in the western hemisphere, where it developed from a tiny, three-toed creature, to the form very much like the one we know today. During the Ice Ages, it migrated across the land bridge into Asia, where it thrived. In America the horse became extinct and didn't reappear here until the Spaniards brought it back as a domesticated animal in the 16th century.The Spanish horses, as are all domestic breeds, were descendants of the wild horses which migrated from America. That original breed still exists. It is called Przewalski's horse, named for the naturalist who first brought specimens to Europe from the grasslands of Mongolia. This is the only true wild horse left in the world. All other so-called "wild" horses are feral animals, that is, horses descended from domestic animals which escaped from or were released by their owners. Przewalski's horses once existed in large herds, but human intrusion into their habitat pushed them farther and farther back into a harsh environment where even these tough animals could not survive.They were last seen in the wilderness in 1967. Fortunately breeding groups existed in zoos and reserves. Captive propagation brought the population up to about 700 by 1985, and four dozen Przewalski's horses have been born at the San Diego Zoo and the San Diego Wild Animal Park. Several of the Zoological Society's Przewalski's horses are on breeding loans to other zoos.The Eurasian bison, called a wisent, is closely related to the American bison. Although never so numerous as the American member of the species, wisent used to roam the forests which covered western Europe. Centuries of cutting destroyed all but a small remnant of these forests and came within 17 animals of exterminating the wisent. A captive breeding program saved them and today a few hundred live in the Bialowieza Forest in eastern Poland. The San Diego Zoo has produced 25 calves.If the felling of Europe's forests meant the destruction of many wild animal species, it worked to the advantage of others. Deer, for instance, have thrived and live from the British Isles eastward. Red, roe and fallow deer live in western Europe, sika deer in Japan. Pere David's deer, formerly a native of marshy areas in central China, is extinct in the wild. It exists only in zoos and reserves.The hedgerows of western Europe house many small animal species. There are foxes, rabbits, hares, badgers, ferrets, squirrels and birds. These and other animals have adapted to life in a human-dominated environment. Starlings and sparrows, for example, do so well that they are considered "pest" birds. Until recently, one of Europe's largest birds, the white stork, even nested in the smaller towns and villages. The bird was considered a symbol of good luck, and home-owners built platforms on rooftops for its nests. This practice is no longer common and the stork avoids the towns.The most regal of Eurasia's raptors is the golden eagle, and the bird has figured in history for centuries. Its image was carried by Roman legions as they conquered much of the continent. During the Middle Ages, lesser members of royalty were free to use other raptors for falconry, but the eagle was reserved for the king. Today, in more remote parts of Asia, the golden eagle is used to hunt wild goats, gazelles, foxes, and wolves. The bird occurs in the United States, where it is under federal protection. It can be seen in San Diego's back country and often is observed soaring over the San Diego Wild Animal Park.Several other northern Eurasia predators are found in North America - falcons, hawks and owls; mammals including wolves, wolverines and foxes. a However, two mammalian predators are unique to I the Old World - leopards and tigers. Leopards range i from northern Asia into Africa; tigers live only in Asia I from Manchuria southward into India and Malaysia. There are five races of this great cat; all of them are endangered. The Zoo enjoys considerable success breeding and raising Siberian tigers, of which the total world population is only about 750 individuals. More than two dozen cubs have been born and raised at the Zoo.South of the taiga, Eurasian biomes become less clearly defined. Much of the area is flat and treeless. In the west, where rainfall is adequate, grass grows thickly. But deep in the continent's interior, the land becomes a desert. Here, thousands of miles from the moderating effects of the ocean, temperatures can climb well above 38°C (100°F) in summer, and